We just spent two days in Montreal, mostly eating. As we had two little kids in tow, we had some serious limitations, and sometimes ended up eating places because of location. In general, we ate very well.
Fous Desserts still has the best croissant/pain au chocolat in Montreal in my opinion. We also had a palmier that was excellent. We took some of their beautiful entremets home for dessert later that day - the chocolate eclair was very good, the Gargamel (milk chocolate, caramel, etc) was good but too sweet, the Millefeuille was decent, and the dark chocolate/pear concoction was good, not great).
Lunch at Schwartz's - perfect and satisfying, inexpensive. We don't go everytime we visit Montreal, but often.
We also ate lunch at l'Express. I hadn't been in years, and it was very good. The best was the smoked mackerel and the onglet/frites was very nice. The confit de canard salad was good but too heavy on the salad oil. They were especially nice to us considering we had two tired kids with us.
The Bad (or at least disappointing)
Cafe Sardine's donuts! We trekked all the way up there on foot in the rain, and found their lemon donut no where near fresh. We were assured it was made that day, but if it was, they have a problem as it was only 3 pm - and donuts shouldn't be that stale by that point in the day.
Mamie Clafoutis' viennoiseries were not as good as Fous Desserts. They lacked the light textures and delicacy, and were overly sweet. Their cheddar/leek ficelle however, is very good. Maybe if we stick with savoury products, they are better. We were really sad they didn't have their Kouign Aman, which we have loved in the past.
Kasa Sushi (on Mont-Royal, near Papineau) was our choice due purely to proximity to our accomodation. It was pretty awful - most of the rolls had lots and lots of rice and the thinnest strips of fish I have ever seen. They were miniscule. I feel like we paid for some tempura, a few shrimp and rice. It wasn't dirt cheap, so I don't understand.
I am sad I missed getting to Boulangerie Guillaume, Olivier Potier, and was too full to really enjoy the ice cream at Havre des Glaces. Overall, though, we had a great time and ate very well (certainly better than we would have in Ottawa).
Thanks for all of your good information on the Chowhound board - it has been helpful in making many food plans.